Brake pedal testers are employed to test the braking system of an automotive vehicle. For example, the tester may discover leaks in the hydraulic system. A brake pedal tester now in use is mounted on a fixture and has a test head that engages and presses upon the brake pedal. The fixture is supported on the floor pan of the vehicle and has pins at the rear of the fixture to locate in holes in the floor pan. However, there is nothing to lock the fixture down on the floor pan. The pins establish a rear pivot point such that when the test head is advanced to depress the brake pedal, the fixture will tend to rotate about the rear pivot point, lifting up on the front. The upward pressure on the fixture causes a considerable side load on the test head, producing erroneous test readings and often causing substantial damage to the test head.